Structural evolution and properties of SiC/SiBCN composites at elevated temperatures

The SiC/SiBCN composites were prepared via polymer infiltration and pyrolysis (PIP) technique. The structural composition and property evolution behavior of the composites under inert high-temperature environment were investigated to reveal the failure mechanism of the composites. With the increase of the heat treatment temperature from 1500 degrees C to 1600 degrees C, the composite properties underwent a sharp decline. Among them, the weight loss rate gradually increased from 3% to 9% and the density decreased from 2.4 g/cm(3) to 2.3 g/cm(3). Especially, the room temperature flexural strength decreased from 267 +/- 7 MPa to 179 +/- 3 MPa and the strength retention were 46%. The degradation of SiC fiber properties is the main factor for the decrease in flexural strength of the composites at below 1500 degrees C. When heat treatment temperature above 1600 degrees C, the mechanical properties of SiC fiber dramatically decline, and the SiBCN ceramic matrix initially precipitated Si3N4 crystalline phase leading to a carbothermal reduction reaction. Hence, the mechanical properties of the composite at T > 1600 degrees C deteriorate sharply under the influences of the above two negative factors.